A researcher is interested in investigating how teaching style (structured vs. unstructured) affects learning of vocabulary in children who are developmentally delayed, typically developing and gifted. The researcher organizes an after-school program and all participants are given a pretest. The program consists of 30 minute sessions, two times a week for four weeks. A total of 15 participants are randomly assigned to the high structure class or the low structure class. All classes focus on word knowledge and vocabulary. At the end of the program, ther researcher assesses word knowledge for developmentally delay, typical and gifted students in the low structure group. The researacher is wondering whether the level of structure (high vs. low) might affect the participant groups differently.